The two dry sand samples are examined by changing one parameter. the independent variable, the one that is intentionally manipulated between the two samples, is the (temperature over time , mass of each sample, or type of material used)

the first box is correct

The two dry sand samples are examined by changing one parameter. The independent variable, the one that is intentionally manipulated between the two samples, is the  Mass of each sample

the second box as well

Besides the amount of material, there is also another variable that is manipulated within each of the two mass groups and represented as three types. This independent variable is the type of material used

& the third box

In each case, the dependent variable, the one that you measure the response in, is the temperature over time

i think the answer is a, hope this is right, that would be my best guess.

the minimum amperage that the current in this wire would have to have so that its weight is completely supported by the magnetic force due to earth's field, assuming that no other forces except gravity act on it